86 PROTECTION or PLANTS — 1922-23 



of large numbers advisable if the results are to be of any value for comparative 

 purposes. 



b. EflFect of temperature. 



Within the limits studied (20 c — 28 c) certain facts are quite clear in 

 regard to the effect of temperature. The amount of aerial browth dependas on 

 the temperature but not constantly for all species, in some cases more being pro- 

 duced at higher than lower and vice versa, as, for example, F. gibbosum, which 

 produces more growth at 25 c that at 20 c on Uschinsky's solution, while F. 

 Orthoceras produces more at 20''c. Larger spores may be produced at higher 

 temperatures. A more intensified colour is quite characteristic of the growth 

 at higher temperatures. More fungus material (dry weight) is produced at 

 25*0 than at 20'c. 



Growth at different concentrations of the H-ions in the media. 



In order to secure data on this factor a series of cultures were grown on media 

 (Duggar's and Harshberger s'solutions) standardized to different Ph values. 

 Clarke's colorimetric method was used. 



The experiments brought a number of interesting facts to light. In the 

 first place it is apparent that the effect of the H-ion concentration depends both 

 upon the medium and the organism. F. orthoceras (F and G) shows no diffe- 

 rences in growth characteristics on either Harshberger's or Duggar's solu- 

 tions. The other three species used in this phase of the work, namely, F. 

 martii phaseoli, F. lathyri, and F. gibhosum, show differences but not constant 

 ones, as is shown by the least mentioned organism, which, at the higher Ph 

 values on Harshberger's produces large numbers of macroconidia , while on 

 Duggar's ,at similar values it fails to produce any. This supports the results 

 obtained by Webb (15:1919), and Zeller, Sehmitz and Duggar (17:1919). 



The second interesting fact is in regard to colour production. Within the 

 limits studied colour production does not appear to be related to the H — ion con- 

 centration, but to depend mooe upon the composition of the medium. F. or- 

 thoceras (F and G) and F, martii phaseoli (J) produce a uniform colour on each 

 medium throughout the whole range of Ph values, but a different intensity on 

 each medium in each case. In the case of F. lathyri (D) and F. gidbbosum (K) 

 there seems to be a gradation in the intensity of the colour and the amount pre- 

 sent. It must be remembered, however, that there is a similar gradation in the 

 amount of growth exposed to free air in these cultures. Whether this gradation 

 is due to the increasing Ph values or not is a question. The character is so 

 variable that a definite conclusion is impossible. It appears, however, that the 

 colour intensity depends on the amount of free air present rather than on the 



